Horizontal directional drilling tool with return flow and method of using same

ABSTRACT

A horizontal directional drilling tool and method for drilling a borehole through a subsurface formation between locations at a surface is disclosed. The drilling tool includes a bit, an outer tube, an inner tube, and rotational drivers. The outer tube is coupled to a surface driver. The inner tube is coupled between the surface driver and the bit to translate rotation therebetween. The inner tube has a drilling fluid passage therethrough, and is positioned within the outer tube to define a return flow passage therebetween. The rotational drivers include propulsors coupled to the inner tube. The propulsors comprise blades extending into the return flow passage and rotationally driven therein whereby returns in the borehole are urged uphole.

BACKGROUND

This present disclosure relates generally to drilling operations. Morespecifically, the present disclosure relates to Horizontal DirectionalDrilling (HDD) techniques used in forming boreholes for the installationof infrastructure lines for utility, distribution, and transmissionunderground infrastructures.

Underground infrastructure lines may be installed between locationsalong surface or subsurface paths. Such underground infrastructure linesmay include power, water, wastewater, fiber optics, gas, orpetrochemical lines. The installation of underground infrastructurelines may encounter obstacles, such as roads, hills, structures, bodiesof water, environmentally sensitive areas, etc. To circumvent suchobstacles, the underground infrastructure lines may be installed byhorizontally drilling subsurface paths between the locations and passingthe underground infrastructure lines through such subsurface paths.

The subsurface paths are formed by drilling boreholes from a firstlocation into subsurface formations and exiting at a second surfacelocation a distance from the first location. In some cases, theboreholes extend a distance between locations below the surface to passbelow the obstacles. For example, the boreholes may be drilled from thefirst location on one side of a river, pass below the river, and exit atthe second location on another side of the river. The undergroundinfrastructure lines are then passed through the borehole to commonlyconnect to infrastructure equipment on both sides of the river.

The borehole may be drilled using drilling equipment including adrilling rig for advancing a drilling tool through the subsurfaceformation. The drilling tool includes a drill string with a bit at adistal end thereof. This drilling equipment may directionally drill theborehole. Examples of drilling equipment are described in U.S. Pat. Nos.7,942,609, 6,854,190, 4,319,648, 5,490,569, 5,209,605, and 4,221,503,the entire contents of which are hereby incorporated by referenceherein.

Despite advances in underground infrastructure drilling, there remains aneed to provide efficient and effective HDD techniques capable ofoperating in a variety of formations and/or preventing damage to theborehole and surrounding formation, such as drill mud frac-outs,collapse, dog-leg-severity, tortuosities, etc., that may occur duringdrilling. The present disclosure is directed at such needs.

SUMMARY

In at least one aspect, the present disclosure relates to a horizontaldirectional drilling tool for drilling a borehole through a subsurfaceformation between locations about a surface. The drilling tool comprisesa bit, an outer tube, an inner tube, and rotational drivers. The outertube coupled to a surface driver. The inner tube is coupled between thesurface driver and the bit to translate rotation therebetween. The innertube has a drilling fluid passage therethrough. The inner tube ispositioned within the outer tube to define a return flow passagetherebetween. The rotational drivers comprise propulsors coupled to theinner tube. The propulsors comprise blades extending into the returnflow passage and rotationally driven therein whereby returns in theborehole are urged uphole.

In another aspect the disclosure relates to a horizontal directionaldrilling system for drilling a borehole through a subsurface formationbetween locations about a surface. The drilling system comprises asurface driver, and a horizontal directional drilling tool. The drillingtool comprises a bit, an outer tube, an inner tube, and rotationaldrivers. The outer tube coupled to a surface driver. The inner tube iscoupled between the surface driver and the bit to translate rotationtherebetween. The inner tube has a drilling fluid passage therethrough.The inner tube is positioned within the outer tube to define a returnflow passage therebetween. The rotational drivers comprise propulsorscoupled to the inner tube. The propulsors comprise blades extending intothe return flow passage and rotationally driven therein whereby returnsin the borehole are urged uphole.

Finally, in another aspect, the disclosure relates to a method fordirectionally drilling a horizontal borehole through a subsurfaceformation between locations about a surface. The method comprises;providing a drilling tool comprising an inner tube, an outer tube, and abit; advancing the bit into the subsurface formation by axially drivingthe outer tube and rotationally driving the bit via the inner tube;passing a drilling fluid through the inner tube and out the bit, thedrilling fluid mixing with cuttings generated by the bit to formreturns; and urging the returns from the borehole to the surface byrotating rotational drivers in a return flow passage between the innertube and the outer tube.

This summary is not intended to limit the disclosure. Other features arecontemplated as set forth further herein.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the above recited features and advantages can be understood indetail, a more particular description, briefly summarized above, may behad by reference to the embodiments thereof that are illustrated in theappended drawings. It is to be noted, however, that the examplesillustrated are not to be considered limiting of its scope. The figuresare not necessarily to scale and certain features and certain views ofthe figures may be shown exaggerated in scale or in schematic in theinterest of clarity and conciseness.

FIGS. 1A-1C are schematic diagrams, partially in cross-section of an HDDsite having HDD equipment with return flow capability for performing HDDoperations including drilling a borehole into a subsurface formation,reaming the borehole, and installing an infrastructure line in theborehole, respectively.

FIG. 2A is a detailed view of a portion of the subsurface formation andthe HDD equipment of FIG. 1A depicting borehole damage (BH damage). FIG.2B is a cross-sectional view of the formation of FIG. 2A taken alongline 2B-2B.

FIGS. 3A and 3B are schematic diagrams, partially in cross-section of anexample of the HDD tool with return flow capability.

FIG. 4 is a schematic diagram depicting a portion 4 of the HDD tool ofFIG. 3A.

FIGS. 5A and 5B are partial, cross-sectional views of a portion 5 of theHDD tool of FIG. 3B.

FIG. 6 is a longitudinal, cross-sectional view of a portion 6 of the HDDtool of FIG. 3B.

FIG. 7 is a longitudinal, cross-sectional view of a portion 7 of the HDDtool of FIG. 3B.

FIG. 8 is a longitudinal, cross-sectional view of a portion 8 of the HDDtool of FIG. 3B.

FIGS. 9A and 9B are partial, cross-sectional views of portions 9A and 9Bof the HDD tool of FIGS. 3B and 3A, respectively.

FIG. 10A is a radial, cross-sectional view of the portion of the HDDtool of FIG. 5A taken along line 10A-10A.

FIG. 10B is a radial cross-sectional view of the portion of the HDD toolof FIG. 7 taken along line 10B-10B.

FIGS. 11A-11B are radial cross-sectional views of HDD tools depictingvarious configurations of stabilizers.

FIG. 12A shows a portion of the HDD tool of FIG. 4 during biasing upwarddrilling.

FIG. 12B is a cross-sectional view of the portion of the HDD tool ofFIG. 12A taken along lines 12B-12B.

FIG. 13A shows a portion of the HDD tool of FIG. 4 during biasingdownward drilling.

FIG. 13B is a cross-sectional view of the portion of the HDD tool ofFIG. 13A taken along lines 13B-13B.

FIG. 14A shows a cross-sectional view of the HDD tool of FIG. 4 duringdrilling at a fixed tool-face orientation.

FIG. 14B shows the cross-sectional view of the HDD tool of FIG. 14Aafter settling of solids about the HDD tool.

FIG. 15A shows a cross-sectional view of the HDD tool of FIG. 14Arotated 180 degrees.

FIG. 15B shows of the HDD tool of FIG. 15A after unsettling of thesolids about the HDD tool.

FIG. 16 is a detailed view of a portion 16 of the HDD tool of FIG. 5Bdepicting a support.

FIG. 17A is a longitudinal, cross-sectional view of a portion 17A of theHDD tool of FIG. 3B having supports.

FIG. 17B is a detailed view of a portion 17B of the HDD tool of FIG.17A.

FIGS. 18A and 18B are side and front views, respectively of a bearinginner race.

FIGS. 19A and 19B are front and side views, respectively, of a bearingouter race.

FIG. 19C is a detailed view of a portion of the bearing outer race withthe anti-rotation pin.

FIG. 20 is a flow chart depicting a method of horizontally drilling asubsurface borehole.

DETAILED DESCRIPTION

The description that follows includes exemplary apparatus, methods,techniques, and/or instruction sequences that embody techniques of thepresent subject matter. However, it is understood that the describedembodiments may be practiced without these specific details.

The present disclosure relates to HDD techniques (e.g., tools, systems,and methods) for drilling subsurface boreholes for the passage ofunderground infrastructure lines (e.g., lines for utility, distribution,and transmission for power, water, wastewater, fiber optics, gas,petrochemical, formation drainage, seawater inlets, etc.) betweensurface locations. The drilling techniques may include an HDD tool withinternal passages for both passing drilling fluid from the surfacethrough the HDD tool and passing returns (e.g., bit cuttings, boreholesolids, borehole fluids, etc.) back to the surface during drilling.

The return flow features of the HDD tool may be used to draw in, breakdown, pass, and/or manipulate returns, to assist in maintaining solidssuspension, and/or to prevent blockage of returns from the borehole tothe surface. The HDD tool may also be configured to control and/ormitigate damage to the borehole and/or surrounding formation, such asfrac-outs, dog-leg severity, tortuosities, borehole collapse, etc. (“BHDamage”). For example, the HDD tool may facilitate removal of thereturns in a manner that seeks to prevent the BH damage. These and/orother features of the HDD tool may be configured to enhance drillingoperations in a variety of non-competent formation conditions subject toBH damage, such as soft, weak, fractured, shallow, and/or unconsolidatedformations, and/or in horizontal (or near horizontal), shallowsubsurface, and/or alluvial weak formations (e.g., soft sands, silts,clays, gravels, or fractured rock, and/or other weak materials).

Frac-outs as used herein refers to the hydro-fracking of the formationsurrounding the borehole and/or the inadvertent release of fluid fromthe borehole into the surrounding formation during drilling. Drill mudfrac-outs may occur, for example, when fluid pressure in the borehole(or annulus pressure) exceeds pressure of the formation (or fluidcontainment of the borehole and/or surrounding formation), and/or wherethe drilling fluid in the borehole finds openings (e.g., as fault lines,fractures, infrastructure, loose material, etc.) along a wall of thebore. These frac-outs can be natural or induced by over pressurizing theformation.

The frac-less HDD techniques provided herein are intended to prevent theBH damage to the formation while facilitating drilling of the subsurfaceboreholes. These frac-less HDD techniques seek to provide one or more ofthe following: isolated drilling fluid and solids return passages,integrated drilling and return components, integrated drilling assembly(e.g., Bottom Hole Assembly (BHA)) and multi-layered drill pipe, urgingreturn flow from the borehole through the BHA and multilayered drillpipe to the surface, clearable fluid passageways, grinding (or milling)during drilling to size and reduce formation cuttings in the returns,measured drilling parameters (e.g., borehole fluid pressure, rate ofpenetration, weight on bit, azimuth, inclination etc.), concentricdrilling fluid and return flow configurations, returns blockage,resistance, protective layering of drilling components, internal devicesand methods for assisting in suspension of returns, wear resistance,induced return flow, maintained tool face orientation during unsettlingof solids, facilitated removal of cuttings, and/or other capabilities.

FIGS. 1A-1C show an HDD site 1, including HDD equipment 2 with returnflow capabilities usable for performing an HDD operation to install anunderground infrastructure line 3. The HDD equipment 2 includes a drillrig 33, a mud pump 34, and solids control 35 positioned at surface 23.The HDD equipment 2 also includes an HDD tool 14 made up of a drillstring 11, a BHA 59, and a bit 25. The HDD equipment 2 may includefeatures of conventional drilling equipment. See, e.g., U.S. Pat. Nos.7,942,609, 6,854,190, 4,319,648, 5,490,569, 5,209,605, and 4,221,503,previously incorporated by reference herein.

The rig 33 may include various mechanisms for connecting the bit 25, BHA59, portions of the drill string 11, and/or other drilling equipmenttogether to form the HDD tool 14. A series of drill pipes may bethreadedly connected together in series by the rig 33 to form thedrilling string 11. The BHA 59 and the bit 25 may be connected at adownhole end of the drill string 11 to form the HDD tool 14. The HDDtool 14 is suspended from the drill rig 33 and advanced into formation17 to form a borehole 12. The rig 33 may include various mechanisms forapplying rotational force and axial force to advance and/or retract theHDD tool 14 and the bit 25. The BHA 59 may include various components tofacilitate drilling, such as a bent axis directional drilling assembly,mud motor, reamers (hole-openers), and/or other components (not shown).

The HDD tool 14 may have a fluid passage therethrough for passingdrilling mud pumped by the mud pump 34 at the surface 23 to the bit 25.The drilling mud exits the HDD tool 14 about the bit 25 as the bit 25engages and removes cuttings from the formation 17. The HDD tool 14 isprovided with return flow capabilities for passing the drilling mud andthe cuttings back to the surface 23 as is described further herein.

The HDD tool 14 may be used to perform various HDD operations. The HDDoperation may include drilling the borehole (or pilot bore) 12 into theformation 17 as shown in FIG. 1A, reaming the pilot borehole 12 to forma reamed borehole 12′ as shown in FIG. 1B, and installing aninfrastructure line (or conduit) 3 in the borehole 12 (and/or the reamedborehole 12′) as shown in FIG. 1C. The drilling the pilot borehole 12 ofFIG. 1A involves advancing the HDD tool 14 into the formation 17 by therig 33. The HDD tool 14 may pass along a predetermined path from a firstsurface location (or entry point) 13 through the formation 17 and to asecond surface location (or exit point) 15 to form the pilot borehole 12of a desired geometry. As shown, the path may be an arcuate shape pathextending below an obstacle, such as a body of water 19. The pilotborehole 12 may have a given length, such as in excess of about 5,000feet (1524 m), and/or have a diameter of from about 3 inches (7.62 cm)to about 14 inches (35.56 cm).

The drilling of FIG. 1A may be a one-stage HDD operation. In theone-stage HDD operation, the HDD tool 14 may carry a leave in placedrill string 11 into the borehole 12 during drilling. The leave in placedrill string 11 may be used to line the pilot borehole 12. Once theleave in drill string 11 is drilled and at permanent rest within theborehole, now acting as a conduit, one or more of the infrastructurelines 3 may be passed through the leave in place drill string 11.

The drilling of FIG. 1A may be performed in a multi-stage operation. Forexample, in a two-stage operation once the HDD tool exits the exit point15, the HDD tool 14 may be connected to an infrastructure line 3 andretracted back through the pilot borehole 12 by the rig 33 as shown inFIG. 1C. The line 3 may remain at permanent rest within the borehole 12,and be connected to infrastructure equipment on both sides of theobstacle 19.

In another example, in a three-stage operation, the pilot hole 12 isdrilled as in FIG. 1A, As shown in FIG. 1B, once the HDD tool 14 exitsthe exit point 15, the HDD tool 14 may be provided with one or morereamers 26, each reamer being of the same or different sizes. The HDDtool 14 then may be passed through the borehole 12 to the entry point 13with the reamer 26 attached thereto to increase a diameter of the pilotborehole 12 to an expanded borehole 12′ using the reamer 26. Multiple,or greater diameter line/s 3 may then be installed in the reamedborehole 12′ as demonstrated by FIG. 1C.

The HDD operations of FIGS. 1A-1C may be performed manually and/orautomatically operated. The HDD tool 14 may be provided with sensors Sand a surface unit 38 to collect measurements during the HDD operations.Based on the sensed measurements and/or other data, adjustments may bemade to the HDD operations.

While FIGS. 1A-1C shows a three stage service HDD operation, the serviceoperation may involve one or more stages, various combinations of thestages, and/or other tasks. For example, one or more of the servicelines 3 may be installed from either location 13, 15. Other HDDoperations may also be performed, such as drilling from a first surfacelocation (or entry point), under an obstacle, to remain un-surfaced,where the borehole 12 is lined with perforated pipe, to act as aformation fluid drain (see, e.g., U.S. Pat. No. 5,209,605, previouslyincorporated by reference herein). Another drilling operation mayinvolve drilling at a first ground surface location (or entry point),under an obstacle and exit at second location into a body of water. See,e.g., U.S. Pat. No. 6,851,490, previously incorporated by referenceherein.

FIGS. 2A and 2B show the HDD tool 14 operated without return flowtherethrough. In some cases, return flow through the HDD tool 14 may beinactivated such that return flow passes through the annulus between theHDD tool 14 and the wall of the borehole 12. FIG. 2A shows the BHA 59positioned in the borehole 12 with cuttings 29 generated during drillingmixed with drilling fluid 79 to form returns 30. FIG. 2B shows a portionof drilled borehole 12, where cutting 29 settle-out from returns 30. Asshown by these figures, during one or more of the various HDDoperations, the formation surrounding the borehole 12 may be subject tothe BH damage during drilling.

During some drilling conditions, the drilling fluid may pass through theHDD tool 14 and into the borehole 12, and the returns 30 may passsuccessfully out of the borehole 12, through the HDD tool 14, and backto the surface 23 (FIG. 1A). During other drilling conditions, as shownin FIGS. 2A and 2B, the BH damage, such as frac-out 71, may occur in theformation 17 surrounding the borehole 12. When occurring during thedrilling of the borehole 12 as shown in FIG. 1A, this BH damage may beconsidered an inadvertent loss of returns (e.g., frac-outs). Whenfrac-out occurs during other portions of the HDD operation (e.g., thereaming of FIG. 1B), the BH damage may be considered a cause associatedwith initial pilot hole drilling frac-outs. For example, higher borehole(annulus) pressures may occur during the pilot hole drilling (e.g., FIG.1A), which may cause the initial frac-outs and/or weakening of theformation surrounding borehole. This may then lead to further orcontinuing frac-outs during reaming or pipe installation (e.g., FIGS. 1Band/or 1C).

The BH damage to the formation during drilling may be caused by variousnon-competent formation conditions. These non-competent formationconditions may involve certain drilling paths, such as horizontal (ornear horizontal) and/or shallow subsurface, or weak formations, such asalluvial weak formations (e.g., soft sands, silts, clays, gravels, orfractured rock, and/or other weak materials), may be subject tofrac-outs and other BH damage. As the borehole drilling lengthen, thereturns annulus pressure-drop increases, and the ability to evacuate thecuttings 29 from the borehole may diminish and pressure in the boreholemay increase, thereby increasing potential risk of the returns 30 tofrac-out, which may lead to environmental and/or BH damage. Increasedreturns velocity may require higher pressures (e.g., to achieveturbulent flow) and/or may cause erosion, which may also increase therisk of the frac-out or other BH damage, particularly in thenon-competent formations. Erosion may also cause borehole collapseand/or block returns, which may also cause the BH damage. When thedrilled fluid returns flow through the borehole annulus at lowvelocities (e.g., laminar flows), conveyance of solids out of theborehole may be limited, and the entrained solids within laminar flowreturns settle-out. This may also reduce the borehole annulus and causethe returns to become turbulent flow, thereby again increasing boreholeannulus pressure and the risk of frac-outs, which in turn can damage theformation and the surrounding environment. Where the borehole annuluspressure is higher than the surrounding formation, the differentialpressure may result in drag or sticking of the drill string 11 (FIG.1A). Increased viscosity of drilling mud returns may require greaterpressure to force returns throughout the borehole annulus, therebyincreasing the risk of frac-outs that may cause damage to thesurrounding environment and/or the BH damage.

Also, due to thixotropical nature of drilling mud after prolongeddrilling inactivity, static drilling mud returns may gain gel strengthand may require greater pump pressure and time to acquire a flowingstate, thereby requiring increasing borehole annulus pressure andresulting in the risk of frac-outs that may cause BH damage and/or otherenvironmental damage. Increased drill-mud return velocities acrossgreater diameter portions of the HDD tool, such as drill pipetool-joints, drill collars, mud motors, stabilizers, BHA subs, etc., mayincrease annulus pressure, induce differential sticking of the HDDtools, and/or promote frac-outs, which may lead to the environmentaldamage and/or the BH damage. Vibration of the HDD tool (e.g., thePositive Displacement mud Motor (PDM)) may cause erosion (e.g., soilliquefaction) along the borehole, thereby effecting BHA stability and/orreturns flows which may result in the BH damage. Some BH damage, such asexcessive undulations and/or dog-legs that may cause severetortuosities, that may also make it difficult or impossible to installthe infrastructure line, or damage to the infrastructure line and/or itsprotective coatings.

As also shown by FIGS. 2A and 2B, the HDD tool 14 may be operated withreturn flow activated (FIG. 3A-4) or inactivated/conventional mode(FIGS. 2A-2B). In some cases, return flow may be inactivated and/orblocked, while the drilling fluid 79 passes through the inner pipe 77and into the borehole 12. This operation may be similar to conventionaldrilling where the returns 30 may settle solids 31 in the borehole 12 asshown. In this example, the drilling fluid does not return upholebetween the inner pipe 77 and the outer pipe 75. Instead, the drillingfluid 79 passes outside of the outer pipe 75 and into the borehole 12where it may settle out.

FIGS. 3A-3B and 4 depict various views of the HDD tool 14 with returnflow capabilities usable for performing the HDD operations of FIGS.1A-1C. As shown by these views, the HDD tool 14 is supported by the rig33, and includes the bit 25, the BHA 59, and the drill string 11. Thebit 25 is at a distal end of the BHA 59. The bit 25 may be aconventional drag, roller cone, and/or sloped planar jet bit 25 advancedand rotated to cut away portions of the formation (i.e., cuttings 29)and form the borehole 12.

The drill string 11 extends from the rig 33 to the BHA 59 and includesinner pipes 77 and outer pipes 75 threadedly connected in series by therig 33 to form a tubular drill string 11. The inner pipes 77 and outerpipes 75 are axially and/or rotatably drivable by the rig 33. Asindicated by the arrows, the inner pipes 77 and outer pipes 75 may beindependently or integrally coupled to the rig 33 for simultaneous orindependent operation such that the inner and outer pipes 77, 75 arerotated and/or advance/retracted in the borehole 12 as desired. Examplesof rigs and/or drivers that may be used are described in U.S. Pat. No.6,827,158 and 2013/0068490. The BHA, pipes, and/or other portions of theHDD tool 14 may be made of a lightweight materials, such 6000 SeriesAluminum Alloy and/or Titanium Alloy.

The inner pipes 77 and the outer pipes 75 define concentric passages P1,P2 for flow of fluid therethrough. Fluid from the mud pump 34 may passalong passage P1 through the inner pipes 77 and the BHA 59 to bit 25.The returns 30 from the borehole 12 may pass along passage P2 betweenthe inner pipes 77 and the outer pipes 75 back to the surface 23. Thedrilling fluid 79 passing through the HDD tool 14 mixes and entrainswith the cuttings 29 to form the returns 30 that may be pumped throughthe HDD tool 14 and back to the surface 23 for processing through thesolids control 35. The advancement (e.g., axial and/or rotationaldriving) of the HDD tool 14 may be selectively controlled. For example,the advancement may at a ratio between a drilling rate of the advancingdrill-string and a drilling fluid pumping rate of the passing thedrilling fluid through inner pipe 77.

The BHA 59 is supported between the bit 25 and the drill string 11. Asshown FIG. 3A, the BHA 59 comprises distal housing 220 at a distal endof the BHA 59, proximal housing 222 at a proximal end of the BHA, and acoupling housing 221 therebetween. The housings 220-222 may be tubularhousings threadedly connectable to each other and to the outer pipes 75of the drill string 11. The housings 220-22 may be coupled to andoperate as part of the outer pipe 75, collectively referred to as anouter tube.

Each of the housings 220-222 may be provided with stabilizers 162, 163on an outer surface thereof for engagement with a wall of the borehole12. The stabilizers 162, 163 may include adjustable steering stabilizersand/or fixed stabilizers as is described further herein. The proximalhousing 222 externally includes fixed stabilizers 162 and the distalhousing 220 externally includes adjustable stabilizers 163. The BHA 59may also have interior components, such as a tubular shaft 85,propulsors 128, and other BHA components.

The tubular shaft 85 may include one or more tubular shafts (e.g., driveshafts) extending through the housings 220-222 between the drill string11 and the bit 25. A proximal end of the tubular shaft 85 may beconnectable to a distal end of the inner pipe 77 of the drill string 11for fluid communication therebetween and rotation therewith. The tubularshaft 85 may be coupled to and operate as part of the inner pipe 77 ofthe HDD tool 14, collectively referred to as an inner tube. An X-overadaptor 212 may also be provided to connect the distal housing 220 toouter pipe 75 of the drill string 11, and a distal end of the tubularshaft 85 to the inner pipe 77 of the drill string 11. The bit 25 may beconnected to the inner pipe 77 via tubular shaft 85 at the distal end ofthe distal housing 220 for fluid communication therebetween and rotationtherewith.

The propulsors 128 may be positioned along an outer surface of thetubular shaft 85 and extend into the passage P2 between the tubularshaft 85 and the housings 220-222. The propulsors 128 may be bladesattached to an outer surface of the tubular shaft 85, or be integralwith tubular portions connectable to the tubular shaft 85. One or moreof the propulsors 128 may be connected to or part of the inner pipes 77of the drill string 11 and/or the tubular shaft 85 of the BHA 59. Thepropulsors 128 may be fixed to the tubular shaft 85 and rotatetherewith. Such rotation may be used to agitate the entrained bitcuttings 29 of returns 30 as they are urged through a path of thepassage P2 in the housings 220-222. A pipe protector 214 may also beprovided along the inner pipe 77 with blades rotatable with the innerpipe 77 to further facilitate flow, and/or to support the inner pipe 77within the outer pipe 75.

The BHA 59 may be provided with a variety of the interior components forperforming various operations, such as a motor to drive the propulsors128, the tubular shaft 85, and/or the bit 25. The BHA 59 may also beprovided with interior components for performing various functions, suchas sensing, measurement, survey, drilling, power, communication, etc.(see, e.g., sensors S of FIG. 1A).

Fluid circulation is defined along paths extending through the passagesP1 and P2 through the HDD tool 14 as indicated by the arrows. The fluidcirculation includes a drilling fluid path in passage P1 extendingthrough the HDD tool 14, and a fluid returns pathway P2 extending backthrough the drill string 11. The passage P1 of the inner pipe 77 of thedrill string 11 may extend through the inner pipe 77 and the bit 25 forpassage of the drilling fluid 79 through the BHA 59 and out the bit 25.The mud pump 34 may pump drilling fluid 79 through rotatable inner pipe77 of the drill string 11, through the BHA 59, and out the bit 25. Thedrilling fluid 79 may pass into the borehole 12 to mix and entrainedwith the cuttings 29 to form the returns 30.

The returns 30 from borehole 12 may pass back into the HDD tool 14 frominlet 111 behind distal end of shaft 85, pass through passage P2extending between the tubular shaft 85 and the housings (or BHAsections) 220-222, and between the inner pipes 77 and the outer pipes75. The returns 30 may be urged through passage P2 by rotation ofrotational drivers, such as the propulsors 128, helical pipe protectors214, and supports 90 (including inner bearing races 96 as describedfurther herein with respect to at FIGS. 18A-19C). The returns 30 mayexit the HDD tool 14 at the surface 23 and be passed to the solidscontrol 35 located on the surface 23 for cleaning and reuse.

FIGS. 5A and 5B depict various views of a distal end of the HDD tool 14including the distal housing 220 and the bit 25. As shown in theseviews, the distal housing 220 may be a bearing and stabilizer housingfor supporting the bit 25 and the stabilizers 162, 163 for engagementwith the wall of the borehole 12. The bit 25 extends from a distal endof the distal housing 220. The stabilizers 162, 163 are positionedradially about an exterior surface of the distal housing 220.

The distal housing 220 includes a cone housing 83 and a stabilizerhousing 82. The cone housing 83 is threadedly connected to the distalend of the stabilizer housing 82. A proximal end of the bit 25 iscoupled to the tubular shaft 85 for fluid communication and rotationtherewith. The drill bit 25 and the tubular shaft 85 may be rotatablysupported within the distal housing 220 and independently movabletherein. The tubular shaft 85 has an inner cone 113 with an outer cone114 at a distal end of the cone housing 83. The outer cone 114 has anabrasive angled surface 115 positioned opposite an abrasive angledsurface 116 of the inner cone 113 defining a funnel shaped opening thatdefines a returns 30 inlet 111 therebetween (see, e.g., FIG. 16). Theshaft 85 may be provided with an upset 86 for connection with the innercone 113. The bit 25 is threadedly connected to the distal end of theupset 86, and the inner cone 113 is butted against or fastened to aproximal side of the upset 86 of the tubular shaft 85. The cone housing83 is rotatably fixed to the distal end of the stabilizer housing 82.

The bit 25 has passages therethrough for passing the drilling fluid 79from the tubular shaft 85 and through the bit 25 along the path inpassage P1 as indicated by the arrows. The drilling fluid 79 exiting thebit 25 mixes and entrains with cuttings 29 from the formation to formthe returns 30. As shown, the bit 25 is depicted as a fixed cutter bit,but could be any type of bit capable of cutting away portions of theformation to form the borehole 12.

The inlet 111 is positioned uphole from the bit 25 to receive thereturns 30 as they are generated during drilling. The inlet 111 is influid communication with the path of the passage P2 for passing thereturns 30 uphole through the HDD tool 14 during drilling. The inlet 111is, in part, defined by the inner cone 113, which is rotatably attachedby splines 100 (e.g., fluid filled splines) to a distal end of the shaft85. The splines 100 form spline connections between the shaft 85 and theinner cone 113. The inlet 111 is positioned between the inner cone 113and the outer cone 114, and the inlet 111 is tapered between the angledsurfaces 115, 116 to define a returns grinder to grindingly receive thereturns as the inner cone 113 and outer cone 114 rotate. The inlet 111may be sized and/or shaped to receive returns with a maximum sizesolids, and/or to reduce the size of such solids to pass into thepassage P2.

The stabilizer housing 82 is threadedly connected to coupling housing221. The exterior surface of the stabilizer housing 82 is shaped to passinto the borehole 12 created by the bit 25 with an annulus 17 definedtherebetween. The exterior surface may have depressions, such as reliefslots 137, extending therein. These depressions may be used to providepathways for fluid flow and/or to provide a reduced surface area forcontact (or sticking) with the wall of the borehole 12. The stabilizerhousing 82 may also have connectors, such as bolts 140, for selectivelyconnecting the stabilizer housing 82 and/or its components, and accessholes 84 extending into the stabilizer housing 82. The access holes 84may be, for example, spanner wrench holes disposed through the distalhousing 220 for convenience of tightening or loosening threadedconnections during repair or maintenance.

The stabilizer housing 82 may also have stabilizer pockets 143 extendinginto the exterior surface. The stabilizer pockets 143 may be shaped tooperatively receive the stabilizers 162, 163. The stabilizers 162, 163in this example include fixed stabilizers 162 positioned within thestabilizer pockets, and adjustable stabilizers 163 extendable therefrom.The stabilizers 162, 163, and/or pockets 143, may be provided with seals167 to prevent solids laden fluid flow into the stabilizer pockets 143.The stabilizers 163 may be positioned for engagement with the wall ofthe borehole 12. Further details concerning the stabilizers aredescribed more fully herein with respect to FIGS. 10A-15B.

The stabilizer housing 82 has an inner surface shaped to support thetubular shaft 85 and other internal components of the HDD tool 14therein. In this example, the stabilizer housing 82 has an inner surfaceshaped to receivingly support the tubular shaft 85 therein. The supports90 are positioned between the stabilizer housing 82 and the tubularshaft 85 to define the path along the passage P2 therebetween. The sizeof the supports 90 may be shaped to define the dimensions of the path ofthe passage P2 to permit a volume of fluid flow therethrough. Examplesof supports in the form of bearing races are described further hereinwith respect to FIGS. 16-19C.

The propulsors 128 may be positioned radially about the tubular shaft 85and rotatably supported thereon by splines 134. The propulsors 128 maybe rotatable within the distal housing 220 to urge flow of the returns30 towards the surface. The returns 30 are urged into the inlet 111 anduphole through the distal housing 220 by drawing the returns 30 from theborehole 12 through the inlet 111. The inlet 111 may be shaped to reduceoversized drilled solids that may be entrained within returns 30 and/orto assure the solids in the returns 30 may be conveyed throughout thepath of the passage P2 without blocking any passageways. As the returns30 pass through the path of the passage P2, the returns 30 may providecooling and lubrication for portions of the HDD tool 14, such as thesupports 90.

FIG. 6 shows a detailed view of the coupling housing 221 (portion 6 ofFIG. 3B). As shown in this view, the coupling housing 221 is a unitarypiece threadedly connected between the distal housing 220 and to theproximal housing 222. The coupling housing 221 may be provided withfeatures, such as access plug 193 extending through an outer surfacethereof. The access plug 193 may provide an inlet into the interior ofthe coupling housing 221. The supports 90 may also be provided in thecoupling housing 221 for supporting the tubular shaft 85 therein withthe passage P2 defined therebetween. The coupling housing 221 may alsobe provided with various shapes as needed for manufacturing and/oroperational purposes. As shown in this version, the coupling housing 221has a tapered outer surface and a smooth inner surface. The outersurface has a larger diameter at each end and a narrower diametertherebetween. The inner surface has a constant diameter capable ofreceiving the tubular shaft 85 and other components.

The tubular shaft 85 within the coupling housing 221 includes a seriesof shaft portions 183, 185, 198 threadedly and matingly connectedtogether with the path in the passage P1 extending therethrough. Theshaft portion 183 is spline connected to the propulsor 128 in the distalhousing 220, and threadedly connected to the shaft portion 185 withinthe coupling housing 221. The shaft portion 185 has a propulsor 128integrally or removably connected thereto. The shaft portion 185 isconnected between the shaft portions 183 and 198 for rotation therewith.The propulsor 128 along the coupling housing 221 urge the returns 30uphole through the coupling housing 221 through the path of the passageP2.

Various components, such as seals 189, 190, connections (e.g., spline188, thread 187), grease zerk fitting 192, connection means, and/orother features, may be provided as shown. The seals 189, 190 may be usedto prevent flow of fluid from entering the connection at splines 188,and/or as a relief passageway for trapped and/or pressurized lubricationbetween the shaft portions 183, 185 and 198. The connections along thesplines 188 may be lubricated by way of grease zerk fitting 192 throughan access hole to the removable access plug 193. The shaft portions 183,185, 198 (and other items connected along portions of the HDD tool 14)may be provided with various connection means, such as the threads 187and the splines 188. For example, the shaft portion 198 may have aninlet with splines 188 matably connected to the shaft portion 185 fortranslating rotation therebetween. The splines 188 may allow for thermalexpansion or contraction of the shaft portions 183, 185, 198. In anotherexample, threads 187 may be provided between shaft portions 185 and 183for connection and translation of rotation therebetween.

FIG. 7 shows a detailed view of the portion 7 of FIG. 3B depicting theproximal housing 222. As shown in this example, the proximal housing 222may be a stabilizer housing including a tubular housing threadedlyconnected between the coupling housing 221 and the X-over adapter 212.This proximal housing 222 has fixed stabilizers 162 bolted into thestabilizer pockets 143 of the proximal housing 222 with bolts 140. Theproximal housing 221 has an outer diameter that increases about thefixed stabilizers 162. The fixed stabilizers 162 may have a largerdiameter for engagement with the wall of the borehole 12. The fixedstabilizers 162 may also have a cavity 201 therein for hostingelectronics and/or other devices.

The proximal housing 222 has a tapered inner surface with largerdiameters at each end and a narrow diameter therebetween. The smallerdiameter is shaped to receive the tubular shaft 85 and the largerdiameter is shaped to receive the propulsors 128. The propulsors 128 areconnected to the tubular shaft 85 by the splines 134 for rotationtherewith. The tubular shaft 85 is rotationally supported within theproximal housing 222 by the supports 90 with the path of the passage P2defined therebetween. This portion of the tubular shaft 85 may be aunitary piece with the path through the passage P1 extendingtherethrough. The returns 30 passing through P2 are urged further upholethrough proximal housing 222 by rotation of the propulsors 128.

FIG. 8 shows a detailed view of the portion 8 of FIG. 3B depicting theX-over adapter 212 and a portion of the dual drill string 11. This viewshows the outer pipe 75 with the inner pipe 77 of drill string 11concentrically positioned adjacent the X-over adapter 212 with the pathsof the passages P1, P2 extending thereabout as shown. The X-over adaptor212 is threadedly connected between the outer pipe 75 and the proximalhousing 222. The inner pipe 77 and the tubular shaft 85 each have aconstant diameter which expands at a distal end for connection to theX-over inner sub 211. The X-over inner sub 211 and X-over adaptor 212may be connected with the dual drill string 11 and the proximal housing196 to provide rotation and torque to the propulsors 128 and the drillbit 25.

FIGS. 9A and 9B show views of a helical flow-assist pipe protector 214that may be provided along a portion 223 of the dual drill string 11(see, e.g., portion 9A of FIG. 3B). One or more pipe protectors 214 maybe threadedly or stretched connected along one or more portions of theHDD tool 14. The pipe protectors 214 may be axially spaced along theinner pipe 77 (e.g., one for each inner pipe 77 joint).

The pipe protector 214 may include a tubular member 216 and a helicalblade 218. The tubular member 216 may be a cylindrical member having apassage therethrough in fluid communication with the tubular shaft 85 toallow fluid to continue along the path of the passage P1. The tubularmember 216 may have a diameter larger than the tubular shaft 85. One ormore threaded connectors, such as tool joint 72 may optionally beprovided for connection to the inner pipe 77.

The helical blade 218 extends radially from the tubular member 216. Thehelical blade 218 may be made of a flexible material, such as rubber orrubber like material. The helical blade 218 may rotate with the innerpipe 77 during drilling to further urge returns 30 along path of thepassage P2 between the inner pipe 77 and the outer pipe 75. The pipeprotectors 214 may act as a flow-assist helical pipe protector forurging returns flow, agitating laminar returns flow, keeping solids inflow suspension, and/or acting as a marine bearing. The pipe protectors214 may also be used to prevent wear along the dual drill string 11,such as outside wear of the inner pipe 77 and inside wear of the outerpipe 75 which may be due to differential rotation therebetween.

FIGS. 10A-15B shows various configurations of stabilizers usable withthe HDD tool 14 of FIG. 3B. As shown by these views, one or more variousstabilizers may be used in the HDD tool 14. While each example depictsfour stabilizers, it will be appreciated that the drilling tool 14 maybe provided with one or more stabilizers positioned radially aboutvarious portions of the HDD tool 14. Also, while the fixed stabilizersare depicted as rectangular, fixed (and/or) stabilizers may have variousshapes, such as a spiral shape. The stabilizers may be configured forvarious purposes, such as to provide contact with the borehole wall, toalter the bottom hole assembly (BHA) drilling direction, to follow apredetermined and/or desired borehole path, etc.

FIGS. 10A and 10B show radial cross-sectional views of the HDD tool 14of FIGS. 5A and 7 taken along lines 10A-10A and 10B-10B, respectively.FIG. 10A shows an example of the HDD tool 14 with double-actingadjustable stabilizer (DAS) 160A. The DAS 160A includes a pair of fixedstabilizers 162A1, A2 and a pair of adjustable stabilizers 163A1, A2usable as the stabilizers 162,163 of FIGS. 5A and 5B. The stabilizers162A1,A2, 163A1,A2 are positioned in the pockets 143 of the distalhousing 220, with the stabilizers 162A1,A2, 163A1,A2 on opposite sidesof the distal housing 220.

The fixed stabilizers 162A1,A2 are non-adjustable lowstabilizer/enclosure stabilizers fixed to the distal housing 220. Thefixed stabilizers 162A1,A2 may be used to provide drilling stabilizationto the HDD tool 14. The fixed stabilizers 162A1,A2 may extend a radialdistance beyond the distal housing 220 for engagement with the wall ofthe borehole 12. The fixed stabilizers 162A1,A2 may act as centralizersand/or wear resisters of HDD tool 14 during operation.

The fixed stabilizers 162A1,A2 may also be used to house componentsbeneath an outer surface of the HDD tool 14. The fixed stabilizers162A1,A2 may have the cavities 210 therein for hosting various types ofcomponents 145. The components 145 may be secured within the cavities210 and sealed therein by seals 167. The components 145 may be, forexample electrical components (e.g., a battery pack, sensors,controllers etc.) which may be used to supply electrical needs tocomponents in the HDD tool 14 and/or hydraulic components (e.g., ahydraulic pump, electric motor, valving and controllers) which maysupply hydraulic fluid and/or pressure to the HDD tool 14. As shown inthe example of FIG. 10A, the hydraulic components 145 may be used toprovide flow and pressures to operate the adjustable stabilizers 163A1,A2.

The pair of adjustable stabilizers 163A1,A2 may be physically identicaland linked to produce, in an individual manner, the same radiallyextending applied force to the wall of the borehole 12, to bias thedistal housing 220 to the opposite wall of borehole 12. The adjustablestabilizer/s 163 may be selectively activated from a surface location(e.g., rig 33) to generate radial force against the wall of the borehole12 and orient the HDD tool 14. The adjustable stabilizers 163A1,A2 aremovably positioned in pockets 143 for extension and retraction about theHDD tool 14. The stabilizers 163A1,A2 are radially slidably within theirrespective pockets 143 which are circumferentially 180 degrees set-apart(arrows 50, 51) about the exterior of the distal housing 220.

The adjustable stabilizers 163A1, A2 have pressurized (e.g., inflatable)bladders 176 therein movably supported on a bladder backing plates 177.The bladders 176 each have a bladder valve stem 179 that protrudesthrough the backing plates 177. The bladder valve stems 179 fluidlyconnect the bladders 176 to fluid passageways 180 disposed within distalstabilizer housing 82. The component 145 may be a hydraulic fluid powersource located within fixed stabilizer 162A1, from where hydraulic fluidvolume may be alternatively conveyed through passageways 180 to eitherof the adjustable stabilizers 163A1,A2. This fluid may be used to supplyhydraulic flows and pressures through fluid passageways 181 to or frombladders 176 of the adjustable stabilizers 163A1 and 163A2. The bladders176 may be activated remotely at the surface, for example, by commandsfrom a ground surface driller,

The stabilizers 163A1,A2 are movably connected to the distal stabilizerhousing 82 by steering shoes 170 and draw bolts 182. As an example, bypressurizing bladder 176, steering shoe 170 of adjustable stabilizer163A2 radially extends by applying force against the wall of theborehole 12 as indicated by arrow 50. This force also retracts steeringshoe 170 of adjustable stabilizer 163A1 along drawbolts 182 therebyextending a borehole clearance between the distal housing 220 and thewall of the borehole 12. The force 50 also provides a reactive force asindicated by arrow 51 for the distal housing 220 to freely bias drillingoppositely from the wall of the borehole 12 about arrow 50. The fluidflow and pressures into and out of the bladders 176 may be used toselectively manipulate the position of the stabilizers 163A1,A2 andthereby the distal housing 220 as needed as is described further herein.

FIG. 10B is a cross-sectional view of the proximal housing 222 takenalong line 10B-10B of FIG. 7. This figure shows an example of two pairsof fixed stabilizers 162B1-B4 bolted by bolts 140 to the proximalhousing 222. In this example, the fixed stabilizers 162B1-B4 are innon-adjustable Upper Stabilizer/Enclosures (USE) 160B secured by bolts140 in pockets 143 of proximal housing 222 a distance uphole from thedistal housing 220 of FIGS. 3A and 3B. The USE stabilizers 162B1-B4 aresealed by seals 167 in the pockets 143. In this location, the fixedstabilizers 162B1-B4 may be used to maintain centralized stability ofthe proximal housing 222 within the borehole 12. The USE stabilizers162B1-B4 are also provided with cavities 201 therein for hostingposition components 145, such as three axis magnetometers, three axisaccelerometers, gyroscopes, EM (electromagnetic) systems, boreholepressure gauges, BHA returns pressure sensors, short hop telemetry, datatransmission, and/or other devices.

FIG. 11A-11B show example stabilizer configurations 160C,160D usable inthe distal housing 220 (and/or other locations about the HDD tool 14).As shown by these figures, the stabilizers may be configured fororientating by outer pipe 75 of the HDD tool 14 to a desired tool-facedrill direction from the surface.

FIG. 11A shows a dual DAS configuration 160C including two pairs ofadjustable stabilizers 163C1-C4 extendable using the pressurizedbladders 176 as described with respect to FIG. 10A. This dual DASconfiguration 160C may be provided with surface controlled commandcapabilities that allows for extension and/or retraction of one or moreof the stabilizers 163C1-C4 from all directions. The stabilizers163C1-C4 may be used to provide lateral forces against the boreholewall, thereby biasing the HDD tool 14 in a desired tool-face direction,while drill-string is in rotation and advancing, making bore-hole intoformation.

Any two contiguous adjustable stabilizers of 163C1-C4 may be selectivelyextended to bias HDD tool 14 to desired tool-face direction, while theHDD tool 14 is rotating or non-rotating. In this example, thehydraulics, electronics and/or other devices used to activate thestabilizers 163C1-C4 may be positioned in other housings or portions ofthe HDD tool 14.

FIG. 11B shows a single-acting adjustable stabilizer (SAS) configuration160D including three fixed stabilizers 162D1-D3. Upon pressurizingbladder 176, the adjustable stabilizer 163D laterally extends stabilizershoe 173 from pocket 143 to apply a force (arrow 50) against the wall atposition 180° (arrow 46). This force 50 produces an opposite reactionaryforce (arrow 51) across the distal housing 220 and produces a tool-facedirection (arrow 45), thereby biasing drilling to borehole wall position0° (arrow 45). Periodically, penetration into the formation may bepaused to rotate the outer drill-string to assure suspension of settledsolids from returns 30 which may accumulate within the interior of theHDD tool 14 and dual-pipe drill string as described further herein.

FIGS. 12A and 12B illustrate operation of the DAS configuration 160A ofFIG. 10A. As shown in these figures, the adjustable stabilizers 163A1,A2 may be activated to apply an upward lateral drilling bias to thedistal housing 220. In this example, the adjustable stabilizer 163A2 isorientated to 180° borehole position (arrow 46). The adjustablestabilizer 163A2 is energized by pressurizing bladder 176, therebyextending the adjustable stabilizer 163A2 downward (arrow 50) againstthe wall of the borehole 12. This results in a reactionary force (arrow51) which causes the distal housing 220 to forcefully drill in an upwardtool-face 0° direction (arrow 45).

FIGS. 13A and 13B illustrate a procedure to drill in a downwarddirection. By holding the same orientation as described in Figure FIGS.12A and 12B, the DAS configuration 160A may also be used to apply forcevector (see arrow 50) against borehole wall at 0° borehole position(arrow 45), by energizing adjustable stabilizer 163A1, which in turnproduces a reactionary force (see arrow 51) through distal housing 220and bit 25, biasing drilling downward to an intended 180° direction(arrow 46). The stabilizers 163A1,A2 may be activated at various anglesto steer drilling in a desired direction.

As shown by FIG. 14A, the stabilizers 163A1,A2 may be activated tomanipulate drilling in a manner that disrupts settling of entrainedsolids 31 of returns 30 within the HDD tool 14. As shown in FIG. 14A,the stabilizers 163A1,A2 may be selectively activated to apply forces tothe wall of the borehole 12 and to shift the HDD tool 14 within theborehole 12. As shown in FIG. 14A, the adjustable stabilizers 163A1 maybe oriented within the distal housing 220 to provide a tool-face (arrow47) orientated to a 45° tool-face. The stabilizer 163A1 may then beenergized to laterally bias drilling to this 45° direction at arrow 47.The drilled-mud returns 30 may be conveyed along the path of the passageP2 between outer pipe 75 and inner-pipe 77, as shown in FIG. 14B.

Over a period of time, entrained solids 31 within the returns 30 maysettle-out within a bottom portion of the outer-pipe 75 and restrictreturns flows through the tool. To dislodge and enter the settled solids31 back into suspension, the pair of stabilizers 163A1,A2 may beselectively rotated 180 degrees as shown in FIG. 15A. In this position,the stabilizer 163A2 may be activated along the same arrow 47 tomaintain the drilling 45° tool-face direction while allowing the settledsolids 31, as shown in FIG. 14B, to un-settle into returns 30 flow, asshown in FIG. 15B. The HDD tool 14 may be selectively and periodicallyrotated and re-oriented 180 degrees (or other angle) from the surfaceduring drilling to provide a tool face orientation that also allowsdisruption of the solids 31 within the HDD tool 14.

The DAS configurations with adjustable stabilizers may be operated invarious modes. For example, in one mode, the outer surface of the HDDtool 14 may be orientated to desired tool-face with the adjustablestabilizers are radially positioned to bias the HDD tool 14 to atool-face such that the HDD tool 14 is thrust (or slid) ahead withoutrotation to slide the HDD tool 14 through the borehole.

In another example mode, the adjustable stabilizers may be dynamicallyand forcefully positioned against the borehole wall to bias the HDD toolto a selected tool-face while drill-string is in continuous rotation.The ability to directionally steer, while an outer surface of the HDDtool 14 is in rotation may be used to maintain suspension of the solids31 in the returns 30 are being conveyed throughout the HDD tool 14 anddual pipe drill-string.

With the DAS configurations, it may not be necessary to pause drillingin order to rotate the outer drill-string to suspend the settled solids31. The DAS configurations may be activated by surface command toreorient the HDD tool 14 to another tool-face angle. For example, theouter pipe of the HDD tool 14 may be rotated 180 degrees, therebyrotating the adjustable stabilizers 163A1,A2 to an opposite radialposition. In other words, the pair of stabilizers 163A1,A2 switch radialpositions such that the settled solids within the HDD tool 14 aredisrupted while maintaining the same drilling course.

FIGS. 16-19B show various configurations of supports 90A,90B usable tosupport the tubular shaft 85 (and/or shaft portions 183, 185, 198 ofFIG. 5B), within the HDD tool 14. FIG. 16 shows a detailed view of aportion 16 of FIG. 5B depicting the support 90A as a radial and thrustbearing. FIGS. 17A and 17B show views of the support 90B in the form ofa radial carrier bearing. FIGS. 18A-19B show various views of inner andouter bearing races 96, 99 usable the support 90, 90A, 90B.

As shown in FIG. 16, the support 90A may include circular inner bearingrace 96 and outer bearing race 99 secured to the tubular shaft 85. Theinner bearing race 96 may be rotatably secured to the tubular shaft 85by splines 98, and supported against the stabilizer housing 82 of thedistal housing 220. The outer bearing race 99 may be rotatably fixedwithin housing slot 103 by the anti-rotation pins 95. The supports 90may axially fix the tubular shaft 85 within the distal housing 220 bysecuring the inner races 96 between a shoulder of the distal housing 220and bit shaft locking nut 87 (as shown FIG. 5B).

As shown in FIG. 16, the inner bearing races 96 and outer bearing race99 are positioned along the path of the passage P2 such that flow ofreturns cools and lubricates the bearing disks of the bearing races96,99. The inner bearing race 96 may have an inner diameter positionedin an interference fit about the tubular shaft 85. The bearing races96,99 may be positioned in engagement with the stabilizer housing 82.The anti-rotation pin 95 may extend from the stabilizer housing 82 andinto the outer bearing race 99 to prevent rotation therebetween.

FIGS. 18A and 18B show a ring shaped, rotatable inner bearing race 96(rotatable as indicated by arrows 40). The inner bearing race 96 may beshaped to form a fluid turbine rotor to enhance flow. Passageways 104extend through the bearing race channel 105 to permit fluid to passthrough the path of the passage P2. Surfaces about the passageways 104and/or channel 105 may be shaped like fan or turbine blades to urgefluid flow thereby. As also shown, the passageways 104 may have variousflow enhancing shapes. The inner bearing race 96 may function as a minorpropulsor element to further urge flow of the returns 30 through the HDDtool 14. Radial bearing disks 106A and thrust bearing disks 106B mayalso be provided along the inner bearing race 96 to matingly bearsagainst radial bearing disks 108A and thrust bearing disks 108B of outerbearing race 99.

FIGS. 19A and 19B show the outer bearing race 99. The outer bearing race99 may be disposed within cavity 102 of the distal housing 220 androtatably fixed by anti-rotation pin 95 such that the returns 30 passthrough passageways 101 of the outer bearing race 99 (see, e.g., FIGS.19A,19B). The outer bearing race 99 may have the housing (oranti-rotating docking) slot 103 for receiving the anti-rotation pin 95.The outer bearing 99 may be provided with radial/thrust bearing disks108A,B for wear. The bearing disks 106A,B and 108A,B may be made of ahardened material for wear resistance and to provide a bearing surfacewith a low coefficient of friction therebetween.

FIGS. 17A and 17B show another support 90B usable as the support 90. Inthis version, the support 90B is a radial bearing assembly including aninner bearing race 96 and an outer bearing race 93 supported along theshaft portion 185 of the tubular shaft 85 in the coupling housing 221.Inner bearing race 96 is rotatably fixed, by splines 98, to rotatablythe shaft portion 185. Outer bearing race 93 is rotatably fixed, byanti-rotation pin 95, to coupling housing 221. The bearing disks 108Amay also be provided along the outer bearing race 93 to bear againstbearing disks 108A along the inner race 96. A portion of the returns 30may flow through multiple fan or turbine shaped passageways 104 formedwithin inner bearing race 96. A portion of the returns 30 may flowpasses through and around bearing disks 106A, 108A for lubrication andcooling thereof.

FIG. 20 is a flow chart depicting a method 2000 of directionallydrilling a horizontal bore (or subsurface borehole). The method 2000involves 2002—providing a drilling tool comprising an inner tube, anouter tube, and a bit; 2004—advancing the bit into the subsurfaceformation by axially driving the outer tube and rotationally driving thebit via the inner tube; 2006—passing a drilling fluid through the innertube and out the bit, the drilling fluid mixing with cuttings generatedby the bit to form returns; and 2008—urging the returns from theborehole to the surface by rotating propulsors (and/or other rotationaldrivers) in a return flow passage between the inner and outer tubes. Theurging may involve 2007—providing supports with passage having flowassist surfaces between the inner tube and the outer tube and rotatingthe supports with the inner tube, and 2009—grinding the returns bypassing the returns through an inlet between the inner tube and theouter tube.

The method may also involve 2010—selectively steering the drilling toolby radially extending stabilizers from the drilling tool,2012—unsettling returns during drilling in the drilling tool byselectively rotating the drilling tool and extending stabilizers aboutthe drilling tool, 2014—unsettling the returns during drilling byselectively rotating the outer tube relative to the inner tube,2016—independently rotating the inner tube and the outer tube and/orcoupling portions of the inner tube together via splines, and/or2018—positioning a flexible pipe protector between the inner tube andthe outer tube. Other features may be provided, such as controlling aratio between a rate of the advancing and a rate of the passing.

The method may also involve controlling a ratio between a rate of theadvancing (e.g., rate of penetration during drilling) and a rate of thepassing (e.g., a rate of drill-fluid input flow through the bit). Thedrilling and fluid parameters may be sensed, regulated, and/orcontrolled to manage a selected ration between the rates. The ROP (rateof penetration) during drilling of soft horizontal boreholes, withoutsufficient volume of drilling mud applied to the bit cuttings willoverload returns with solids. Returns overloaded by solids, requiresgreater pressure to move returns, thereby inducing damage to theborehole and frac-outs. A common soft ground drilling occurrence iswhere the ROP increases, but volume of in-put drilling mud remainsunchanged, whereby returns along returns passageway, becomesinconsistent and flow problematic.

Part or all of the method 2000 may be performed in any order, andrepeated as desired.

While the embodiments are described with reference to variousimplementations and exploitations, it will be understood that theseembodiments are illustrative and that the scope of the inventive subjectmatter is not limited to them. Many variations, modifications, additionsand improvements are possible. For example, various combinations of oneor more of the features provided herein may be used.

Plural instances may be provided for components, operations orstructures described herein as a single instance. In general, structuresand functionality presented as separate components in the exemplaryconfigurations may be implemented as a combined structure or component.Similarly, structures and functionality presented as a single componentmay be implemented as separate components. These and other variations,modifications, additions, and improvements may fall within the scope ofthe inventive subject matter.

Insofar as the description above and the accompanying drawings discloseany additional subject matter that is not within the scope of theclaim(s) herein, the inventions are not dedicated to the public and theright to file one or more applications to claim such additionalinvention is reserved. Although a very narrow claim may be presentedherein, it should be recognized the scope of this invention is muchbroader than presented by the claim(s). Broader claims may be submittedin an application claims the benefit of priority from this application.

Plural instances may be provided for components, operations orstructures described herein as a single instance. In general, structuresand functionality presented as separate components in the exemplaryconfigurations may be implemented as a combined structure or component.Similarly, structures and functionality presented as a single componentmay be implemented as separate components. These and other variations,modifications, additions, and improvements may fall within the scope ofthe inventive subject matter.

What is claimed is:
 1. A horizontal directional drilling tool for drilling a borehole through a subsurface formation between locations about a surface, the drilling tool comprising: a bit; an outer tube coupled to a surface driver; an inner tube coupled between the surface driver and the bit to translate rotation therebetween, the inner tube having a drilling fluid passage therethrough, the inner tube positioned within the outer tube to define a return flow passage therebetween; and rotational drivers comprising a series of propulsors positioned along the inner tube, each of the propulsors comprising blades circumferentially distributed about a portion of the inner tube, each of the blades extending into the return flow passage and rotationally driven therein whereby returns in the borehole are urged uphole.
 2. The drilling tool of claim 1, wherein an inlet to the return flow passage is defined between the outer tube and the bit to receive returns from the borehole.
 3. The drilling tool of claim 2, wherein the outer tube has an outer cone and the bit has an inner cone, the inlet positioned between the inner cone and the outer cone.
 4. The drilling tool of claim 3, wherein the inner cone and the outer cone each have an angled surface, the inlet tapered between the angled surfaces to define a returns grinder.
 5. The drilling tool of claim 1, wherein the inner tube has an upset on a distal end thereof and the bit has an inner cone having an opening to receive the upset.
 6. The drilling tool of claim 2, wherein the inlet to the return flow passage is defined between an angled inlet surface of the outer tube and an angled outer surface of the bit, the inlet having a narrowing tapered shaped to break down cuttings generated by the bit from the borehole.
 7. The drilling tool of claim 1, wherein the rotational drivers comprise a pipe protector between the inner tube and the outer tube.
 8. The drilling tool of claim 7, wherein the pipe protector comprises a flexible blade rotatably extending from the inner tube, the flexible blade comprising an elastomeric material.
 9. The drilling tool of claim 8, wherein the flexible blade has a helical shape with a flow assist surface.
 10. The drilling tool of claim 1, further comprising stabilizers positionable about the outer tube and engagable with a wall of the borehole.
 11. The drilling tool of claim 10, wherein the stabilizers comprise one of: fixed stabilizers, adjustable stabilizers, and combinations thereof.
 12. The drilling tool of claim 11, wherein the fixed stabilizers are fixedly positioned within a pocket extending into an outer surface of the outer tube, the fixed stabilizers having a cavity therein to storingly receive components therein.
 13. The drilling tool of claim 11, wherein the adjustable stabilizers are radially extendable and retractable from an outer surface of the outer tube.
 14. The drilling tool of claim 13, further comprising an inflatable bladder, backing plate, and draw bolts coupled to the adjustable stabilizers to selectively extend and retract the adjustable stabilizers.
 15. The drilling tool of claim 1, wherein a first portion of the outer tube and the inner tube comprises a drill string and a second portion of the outer tube and the inner tube comprises a bottom hole assembly.
 16. The drilling tool of claim 15, further comprising at least one x-over sub coupled between the drill string and the bottom hole assembly.
 17. The drilling tool of claim 15, wherein the outer tube of the bottom hole assembly comprises a distal housing and a proximal housing, with a coupling housing therebetween.
 18. The drilling tool of claim 15, wherein the inner tube comprises tubular shafts connected in series with the drilling fluid passage extending therethrough.
 19. The drilling tool of claim 18, further comprising a spline connection between at least one adjacent pair of the tubular shafts.
 20. The drilling tool of claim 1, wherein the drilling fluid passage of the inner tube is in fluid communication a bit passage through the bit to pass a drilling fluid therethrough.
 21. The drilling tool of claim 1, further comprising supports positioned between the inner tube and the outer tube.
 22. The drilling tool of claim 21, wherein the supports comprise at least one of a radial and thrust bearing, a radial carrier bearing, and combinations thereof.
 23. The drilling tool of claim 21, wherein the supports comprise an inner bearing race and an outer bearing race.
 24. The drilling tool of claim 23, wherein the rotational drivers further comprise flow assist surfaces positioned about flow passages of the inner bearing race.
 25. The drilling tool of claim 21, wherein the inner tube and the outer tube are one of: independently and integrally coupled to the surface driver.
 26. A horizontal directional drilling system for drilling a borehole through a subsurface formation between locations about a surface, the drilling system comprising: a surface driver; and a horizontal directional drilling tool, comprising: a bit; an outer tube coupled to the surface driver; an inner tube coupled between the surface driver and the bit to translate rotation therebetween, the inner tube having a drilling fluid passage therethrough, the inner tube positioned within the outer tube to define a return flow passage therebetween; and rotational drivers comprising a series of propulsors positioned along the inner tube, each of the propulsors comprising blades circumferentially distributed about a portion of the inner tube, each of the blades extending into the return flow passage and rotationally driven therein whereby returns in the borehole are urged.
 27. The drilling system of claim 26, further comprising a mud pump coupled to the drilling tool to pass a drilling fluid through the drilling fluid passage.
 28. The drilling system of claim 26, further comprising a solids control coupled to the drilling tool to receive returns from the return flow passage.
 29. A method for directionally drilling a horizontal borehole through a subsurface formation between locations about a surface, the method comprising: providing a drilling tool comprising an inner tube, an outer tube, propulsors, and a bit, the inner tube positioned within the outer tube to define a return flow passage therebetween; positioning a series of the propulsors positioned along the inner tube, each of the propulsors comprising blades circumferentially distributed about a portion of the inner tube, each of the blades extending into the return flow passage; advancing the bit into the subsurface formation by axially driving the outer tube and rotationally driving the bit via the inner tube; passing a drilling fluid through the inner tube and out the bit, the drilling fluid mixing with cuttings generated by the bit to form returns; and urging the returns from the borehole to the surface by rotating rotational drivers the propulsors in a return flow passage between the inner tube and the outer tube.
 30. The method of claim 29, further comprising selectively steering the drilling tool by radially extending stabilizers from the drilling tool.
 31. The method of claim 29, further comprising independently rotating the inner tube and the outer tube.
 32. The method of claim 29, further comprising coupling portions of the inner tube together via splines.
 33. The method of claim 29, further comprising unsettling returns during drilling in the drilling tool by selectively rotating the drilling tool and extending stabilizers about the drilling tool.
 34. The method of claim 29, further comprising unsettling the returns during drilling by selectively rotating the outer tube relative to a tool face position of the inner tube.
 35. The method of claim 29, further comprising grinding the returns by passing the returns through an angled inlet between the inner tube and the outer tube.
 36. The method of claim 29, further comprising positioning a flexible pipe protector between the inner tube and the outer tube.
 37. The method of claim 29, further comprises providing supports with passage having flow assist surfaces between the inner tube and the outer tube and rotating the supports with the inner tube.
 38. The method of claim 29, further comprising controlling a ratio between a drilling rate of the advancing and a pumping rate of the passing.
 39. A horizontal directional drilling tool for drilling a borehole through a subsurface formation between locations about a surface, the drilling tool comprising: a bit; an outer tube coupled to a surface driver; an inner tube coupled between the surface driver and the bit to translate rotation therebetween, the inner tube having a drilling fluid passage therethrough, the inner tube positioned within the outer tube to define a return flow passage therebetween; supports positioned between the inner tube and the outer tube, the supports comprising an inner bearing race and an outer bearing race; and rotational drivers comprising propulsors coupled to the inner tube, the propulsors comprising blades extending into the return flow passage and rotationally driven therein whereby returns in the borehole are urged uphole.
 40. The drilling tool of claim 39, wherein the rotational drivers further comprise flow assist surfaces positioned about flow passages of the inner bearing race.
 41. A horizontal directional drilling tool for drilling a borehole through a subsurface formation between locations about a surface, the drilling tool comprising: a bit; an outer tube coupled to a surface driver; an inner tube coupled between the surface driver and the bit to translate rotation therebetween, the inner tube having a drilling fluid passage therethrough, the inner tube positioned within the outer tube to define a return flow passage therebetween; adjustable stabilizers positionable about the outer tube and engagable with a wall of the borehole; the adjustable stabilizers comprising an inflatable bladder, backing plate, and draw bolts to selectively extend and retract the adjustable stabilizers; and rotational drivers comprising propulsors coupled to the inner tube, the propulsors comprising blades extending into the return flow passage and rotationally driven therein whereby returns in the borehole are urged uphole.
 42. A method for directionally drilling a horizontal borehole through a subsurface formation between locations about a surface, the method comprising: providing a drilling tool comprising an inner tube, an outer tube, and a bit; advancing the bit into the subsurface formation by axially driving the outer tube and rotationally driving the bit via the inner tube; passing a drilling fluid through the inner tube and out the bit, the drilling fluid mixing with cuttings generated by the bit to form returns; urging the returns from the borehole to the surface by rotating rotational drivers in a return flow passage between the inner tube and the outer tube; and unsettling returns during drilling in the drilling tool by selectively rotating the drilling tool and extending stabilizers about the drilling tool. 